Microbes (microscopic organisms that humans live with every day) can survive in much more extreme environments than previously believedplaces of superheated temperatures, radiation, freezing cold, high salt concentrations, or extreme dryness.

"The science we've been operating on, gathered during the Viking 1 and 2 missions in the 1970s, is completely outdated," said University of California planetary scientist David Paige. Paige is also a member of the private, nonprofit NRC.

NASA's Viking landers were the first spacecraft to land on Mars and conduct scientific research. Viking 1 and Viking 2 landed on July 20 and September 3, 1976, respectively.

"The planetary protection policies that we have are rooted in the era of Viking. ," Paige said. "Since then we've found that microbes are a lot more rugged than we originally thought," he added. "In addition, Mars might be more hospitable to life than we originally thought." For example, scientists have found evidence that there could be liquid waterwhich is necessary for life on Earthat many places on the Mars. (See a photo of a "frozen sea" on Mars.)

Scaled-Back Sterilization

The early spacecraft that landed on Mars were thoroughly sterilized. But as money for the space program got tight, the expensive cleansing process was cut back.

Now that more is known about both Mars and microbes, the NRC is advising NASA to develop and implement new methods and rules to detect and eliminate microorganisms on robotic spacecraft. The techniques currently used to clean spacecraft only detect heat-resistant and spore-forming bacteria. The scientists are concerned that NASA's screening-and-cleaning process does not detect all the microbes that might be present on the spacecraft.

The advisory, which is based on a NASA-funded report by the NRC, recommends that all future landers be 100 percent sterilized. The NRC also suggests that NASA undertake a research program to find and test improved techniques within the next three years.